The present invention relates to devices for reducing the pedal travel required to apply the brakes in a powered braking system and in particular to a device which utilizes a hydraulic booster and modulating valves associated with an antilock braking system to reduce the pedal travel required during normal braking.
The brakes of a vehicle are primarily a pressure responsive device in contrast to, for example, an accelerator which is a motion responsive device. Various mechanical characteristics of a braking system such as volume and movement of wheel cylinders required to bring the brake shoes into contact with a drum or rotor, expansion of flexible brake lines and movement between the open and closed positions of the piston of a master cylinder relative to a fill orifice, inherently cause some amount of pedal movement before braking pressure builds. This characteristic will be further increased in dual or split braking systems. Conversely, experience has shown that drivers prefer to have some degree of movement of the brake pedal during use so that the brakes will exhibit a desirable degree of "feel". Heretofore, various devices have been proposed to provide a means to produce a braking system that does not exhibit excessive pedal movement and which simultaneously provides a desired degree of feel.
Simultaneously, anti-lock or adaptive braking systems have now been developed, such systems incorporating sensors, a computing circuit, and a plurality of modulating valves for automatically controlling the application of braking pressure in response to an incipient skid condition of a vehicle's wheels. Such systems typically incorporate a power booster in the form of a motor driven pump and an accumulator to provide power boost during normal braking operation and to provide a source of pressurized fluid during adaptive braking operation.
Broadly, the present invention utilizes existing adaptive braking hardward including the pump-accumulator, brake switch, hydraulic booster, and modulating valves in cooperation with the adaptive braking control to provide a braking system having reduced brake pedal travel during normal non-adaptive braking operation. In a specific embodiment of the invention, actuation of the conventional brake switch provides an input signal to the adaptive braking control. The control, in response to the signal, actuates the isolation valves of one of the hydraulic circuits of the adaptive braking system and the build valves of that hydraulic circuit to connect same to the hydraulic booster. The hydraulic circuit, thus actuated, operates as a full power hydraulic circuit. Because of the volumetric capacity of the pump and accumulator, the additional displacement required to bring the activated hydraulic circuit to the pressure operating portion of its operation is satisfied by the pump and accumulator. This eliminates movement of the brake pedal required to bring the activated hydraulic circuit to its pressure operating state. Because the system operates upon actuation of the brake switch, adjustment of the brake switch operating point can be utilized to provide any desired movement and corresponding degree of feel for the braking system without the need for any physical modification of brake components and without the need for any physical modification of brake components such as spring rates, piston diameters and the like.
It is therefore an object of the invention to provide an improved braking system having reduced pedal travel.
Another object of the invention is to provide such a system which utilizes existing anti-lock braking system hardware to reduce brake pedal travel during normal braking operation.
Still another object of the invention is to provide such a system which utilizes a brake switch in conjunction with anti-lock braking components to provide a system exhibiting reduced brake pedal travel.
Another object of the invention is to provide a braking system in which the pump, accumulator, hydraulic booster, isolation and build valves, and electronic control unit of an anti-lock braking system are utilized to operate at least one hydraulic circuit of the braking system as a full power braking system during normal braking operation.
Still another object of the invention is to provide such a system in which the pedal feel can be controlled by adjustment of a standard brake switch.